Cruise ships are seeing a rise in norovirus outbreaks this year, with 13 reported so far, according to the Centers for Disease Control and Prevention. Ten of the outbreaks have been linked to norovirus, already topping pre-pandemic levels and on track to surpass last year's total of 18.

Health officials believe a new strain of the virus, which has been driving outbreaks on land, may also be fueling the spike at sea. Ships often mirror what happens on land, the CDC said. Between August and early April, states in the CDC's NoroSTAT network reported more than 2,400 outbreaks — nearly double the number from the previous year.

While cruise ships account for only about 1% of norovirus cases overall, the close quarters and shared spaces make it easier for the virus to spread. The CDC reminded travelers that soap and water work better against norovirus than hand sanitizers and urged frequent handwashing.

The CDC's Vessel Sanitation Program remains in place to monitor and investigate outbreaks, even after staffing cuts at the Department of Health and Human Services. When cases spike onboard, cruise lines are required to step up cleaning, isolate sick passengers and crew, and sometimes delay the start of the next trip to disinfect terminals.

The Cruise Lines International Association said outbreaks remain rare and cruise lines continue to follow strict health guidelines worked out with public health agencies.

Before COVID-19, cruise ships typically saw 10 to 11 gastrointestinal outbreaks a year, with norovirus behind most cases, according to CDC data.